Secondary specific immune response in vitro to MSV tumor cells.

The interactions which occur between antigenic tumor cells and normal or immune lymphoid cells in a 3-day in vitro culture, have been studied with a murine sarcoma virus (MSV)-induced tumor. The 3H-thymidine incorporation of lymphoma cells growing in suspension, and the radioactive-chromium release of freshly sampled lymphoma cells regularly added to the culture, have been compared to determine the part played by immune lymphoid cells in cytolysis and cytostasis of the tumor-cell population. The cytolytic activity increases in the culture from day 0 to day 3. It is due, predominantly, to T-cells, and remains specific to antigens shared by MSV tumors and related lymphomas. This activity would be difficult to detect unless freshly sampled ascitic cells were used as targets, since the lymphoma cells spontaneously lose a part of their sensitivity to immune cytolysis during in vitro culture. The method used in the present experiments is a secondary chromium release test (SCRT), which measures the invitro secondary stimulation of cytotoxic T-lymphocytes (CTL) by tumor cells. In the absence of stimulatory cells, the CTL activity would have rapidly fallen in vitro. The cytostatic activity also increases during the 3 days in vitro, in parallel to the cytolytic activity: it is due to non-T-cells and remains mainly non-specific. The significance of these data for the interpretation of invitro demonstrated cell-mediated anti-tumor immune reactions is briefly discussed, as well as their relevance in the in vivo role of immune CTL.